ORIGINAL: grbaker
Like Thomas said, you need to lube the o-rings in the brakes, but go to a store that sells pool supplies and buy a small tube or bottle of silicone o-ring lube.
If you lube the o-rings and still have a problem (and everything else in the system is OK), you can try placing an airline restrictor in the airline to both brakes (1 on each side). I usually place the restrictors just a couple of inches from the brake hub. This slows the activation of the brakes but does still allow full air pressure to them.
I was going to suggest these two as well.
Also, how about 1. a proportional braking system as well (most electronic ones are) and 2. manually "pumping" the brakes to slow the jet down instead of just hitting the brakes and letting them stay on. A gyro will help keep the jet straight even with uneven braking.
Raf